This invention relates to a fuel injector for use in supplying fuel, under pressure, to a combustion space of a compression ignition internal combustion engine.
In order to reduce emissions levels and noise, it is known to provide fuel injectors in which the total area of the openings through which fuel is delivered can be varied, in use. One technique for achieving this is to use two valve needles, one of which is slidable within a bore provided in the other of the needles to control the supply of fuel to some of the outlet openings independently of the supply of fuel to others of the outlet openings.
Such arrangements have the disadvantages that fuel may be able to flow between the inner and outer needles giving rise to substantially continuous delivery of fuel at a low rate. Further in order to control the movement of the inner and outer needles, separate actuators may be required resulting in the injector being of increased complexity.
According to the present invention there is provided an injector comprising a first, outer valve needle, a second, inner valve needle slidable within a passage provided in the outer valve needle, and load transmitting means whereby movement of the outer valve needle can be transmitted to the inner needle.
The load transmitting means may comprise a shoulder associated with the first needle which is engageable with an enlarged diameter region of the second valve needle to restrict movement of the second needle relative to the first needle such that movement of the first needle beyond a predetermined distance causes movement of the second needle.
The shoulder is conveniently defined by an end of a tubular sleeve carried by the first needle and defining part of the passage within which the second needle is reciprocable. The sleeve may project beyond an end of the first needle, and may be arranged to engage the first seating.
Alternatively, the shoulder may be defined by a stepped region of a bore formed in the first needle and defining the passage, the enlarged diameter region of the second needle being compressible to permit assembly.
The inner needle is preferably resiliently biased towards the second seating.
The inner needle is conveniently resiliently biased by a spring.
The biasing of the inner needle ensures that, at the commencement of movement of the outer needle away from the first seating, the inner needle is in engagement with the second seating. Undesirable delivery of fuel through the second outlet opening can thus be avoided.
In an alternative arrangement, the second valve needle is provided with a plurality of flexible members which are deformable between a deformed state and an undeformed state, whereby in the undeformed state the flexible members define the enlarged diameter region of the second valve needle and engage with the shoulder associated with the passage to restrict movement of the second valve needle relative to the first valve needle.
The provision of a second valve needle with a plurality of flexible members provides the advantage that no tubular sleeve component is required. Furthermore, deformation of the flexible members into the deformed state enables insertion of the second valve needle into the passage. Assembly of the fuel injector is therefore simplified and manufacturing costs are reduced.
The second valve needle conveniently comprises an upper body portion and a lower body portion, the flexible members being formed along the length of lower body portion. Preferably, the second valve needle comprises four flexible members defined by apertures formed in the lower body portion of the second valve needle, the flexible members therefore being integrally formed with the second valve needle.
The second valve needle may further include integral resilient bias means for resiliently biasing the second valve needle towards the second seating. For example, the upper body portion of the second valve needle may have a plurality of recesses formed therein, the upper body portion thereby providing a spring function to resiliently bias the second valve needle towards the second seating. The recesses are preferably formed on alternate sides of the second valve needle along the length of the upper body portion.
By integrally forming the resilient bias means with the second valve needle, the number of fuel injector parts is reduced and manufacture and assembly of the fuel injector is simplified.
The load transmitting means may, alternatively, take the form of a pin carried by one of the needles, the pin extending through a slot provided in the other of the needles such that movement of the outer needle beyond a predetermined position can be transmitted to the inner needle. Clearly, in such an arrangement, movement of the inner needle is dependent upon the distance moved by the outer needle, which can be controlled by a single actuator. In an alternative arrangement, such control of movement of the inner needle to be dependent upon the distance moved by the outer needle can be achieved using a hydraulic link rather than using a pin.
In a further alternative arrangement, the load transmitting means may take the form of a hydraulic link arranged such that movement of the inner needle is dependent upon the rate of movement of the outer needle. The hydraulic link conveniently comprises a chamber defined between the inner and outer needles, the chamber communicating through a restricted flow path with a source of fuel under pressure. In use, if the outer needle lifts slowly, fuel is able to flow to the chamber at a sufficiently high rate to prevent movement of the inner needle. Movement of the outer needle at a higher rate is transmitted to the inner needle as fuel cannot flow to the chamber at a rate sufficient to keep the inner needle in engagement with its seating.
According to a second aspect of the invention there is provided a fuel injector comprising a first valve needle reciprocable within a bore formed in a nozzle body and cooperable with a first seating to control the supply of fuel to a first fuel outlet and a second valve needle reciprocable within a passage located within the first valve needle and cooperable with a second seating to control the supply of fuel to a second fuel outlet, the second valve needle comprising resilient bias means for resiliently biasing the second valve needle towards the second seating, the resilient bias means being integrally formed with the second valve needle.